OPPOSITION TO OVERSIZED HINGE PINS

You will find ill-founded opposition to oversize hinge pins on the E.A. Brown site and of course from Thompson Center Arms..

Here is the truth of the matter.

E.A. Brown's Position Statement On Oversize Hinge Pins

Brown says don't use them. TC says, quote, they are a "bunch of crap. VOIDS Warranty" To which I have to respond: Ignorance can be fixed, stupidity cannot.

E.A. Brown's opinion of oversize hinge pins is based, so far as I know, on primarily ONE incident where a machinist reamed a hole, apparently not following my instructions or using the tooling we supply for reaming hinge pin holes.

The owner of the barrel never would send the barrel to me as requested, but sent it back to Brown, so I never had a chance to examine what was actually the situation.

In the last 20 years of selling oversize hinge pins by the thousands, I can only think of THREE instances where a hole was reported to be reamed oversize to accommodate an oversize hinge pin NEEDED to affect a proper fit at the hinge, ie, not shaking and rattling around.

The first was by a "papered" engineer on "Operation Overthink" who reamed both the barrel and frame together and managed to wallow out the barrel hinge pin hole. I sleeved this hinge pin hole and restored the barrel to perfect working order.

The second was a fluke in which part of the problem was one particular batch of .376" diameter reamers miked a bit oversize and probably with a less than steady hand produced an oversize hole..... again, I sleeved the barrel hinge pin hole and solved the problem.

The third was the .300 Win. Mag. that was the cause of Brown's position against oversize hinge pins.

The machinist who did the work MAY have relocated the centerline of the hinge pin hole. It IS possible, especially if machine reamed without a perfect setup and with a chuck or collet with runout in it.

From all the work I have done on factory barrels over the last nearly 28 years, I find that it is the machine reaming of the hinge pin holes in the factory barrels that causes the problem with:

1) Holes that are not the same diameter all the way through,

2) Very commonly, frame hinge pin holes that are larger in diameter on one side of the frame than the other, and

3) Holes that are not even round.

In 1) above, any runout in the reamer will cause it to cut oversize until the radial lands behind the cutting edges stabilize the reamer, after which it will cut pretty close to its true diameter. Thus the hole is larger where the reamer starts in and smaller where it exits.

You find the same thing in gun barrel bores. Where the bore reamer starts in, normally from the muzzle end, it cuts larger. To some degree you get this same thing when a bore reamer exits at the muzzle. Without a major portion of its length being supported, it tends to cut larger. This is why barrel blank manufacturers tell you to trim at least an inch from the muzzle end. And of course the chamber cuts out any flaring at the breech end.

Likewise in 2) above, the reamer cuts larger going in one side and with its radial lands stabilizing it/minimizing the runout, it cuts smaller on the opposite side.

In 3) above, it is very common to chase a few ten thousandths from a hole with a hand reamer and see where it only removes the bluing in the hole in three areas approximately 120 degrees apart, clearly showing the hole is not round.

The matter of headspace: Brown's .300 Win. Mag. customer may indeed have relocated the hinge pin hole while "reinventing the wheel" instead of following my regimen. However, the "order of magnitude" for headspace error is a huge one built into the belted mag system, which Brown only understands in relation ship to a steel headspace gauge, not the actual distance from the CARTRIDGE CASE HEAD to the firing pin bushing.

I tried to discuss this with him, and it was obvious he was not hearing anything I said. Headspace is ALWAYS a function of three basic components, not any one taken alone.

With any given barrel headspace is a matter of:

1) how deep the chamber is cut in the barrel,

2) the length of the ammo referenced from the point that stops its forward movement in the chamber, and

3) the location of the hinge pin holes in the frame.

Each component part has its own tolerance range.

SAAMI says maximum headspace, the distance from the case head to breech face, is .006."

The ammunition manufacturer wants his ammo to fit in all the chambers out there, so he makes the ammo shorter than maximum. Then you find there are several thousandths difference in hinge pin hole locations in the frames. If you don't believe this, then measure the barrel-to-frame gap with the same barrel on a number of frames. You will find upwards of .004" variation.

Now, adding it up:

.006" allowance in the chamber,

.006" allowance in the ammo, and

.004" variation from one frame to the next.

This adds up to a possible .016" actual headspace AND STILL HAVE EACH COMPONENT PART IN SPEC! YET BROWN AND TC BOTH REMAIN BLIND TO THESE VERY EASILY DEMONSTRATED FACTS! FACTS THAT ANY LAYMAN CAN MEASURE HIMSELF AND VERY READILY CORRECT!

(In the menu list, find "Headspace, How To Get It Right.") And since the belt height on belted mag ammo is often as much as .010" LESS than minimum, the situation can be even far worse, yet Brown does not even touch on headspace issues like this. 

 Now, with a modicum of understanding of reamers, tool pressures, and how it all works, it should be clear that the likelihood of being physically able to move the hinge pin hole centerline even .006" is virtually impossible by hand. It simply does not work that way! 

 You CAN do it by holding the part off center and plunging a reamer in since it has an abrupt leade on the end, but it takes a significant force off center to relocate a hole. But this must be forced by machine, not by hand. 

 Reamers work on the basis of equal opposing forces between the cutting edges. They "want" to follow the existing hole. It takes a force overcoming the force on the opposite edge to move the reamer off axis.

In Conclusion:

Fretting over the chance of moving the hinge pin hole centerline a miniscule amount and then ignoring the actual magnitude of headspace parameters is to say the least, ill-informed and short sighted.

A policy such as the one made by Brown, who to my knowledge is not doing machine work himself but rather paroting what someone tells him, on an isolated incident done incorrectly in the first place is a disservice to those who struggle with accuracy issues related to movement of the barrel during the firing cycle.

For every one person taking his position, there are 10s of thousands of shooters who have benefitted from improving the fit between barrel and frame via a very slightly larger hinge pin, seldom requiring reaming of either the barrel or frame hinge pin holes.

And for those extreme situations that DO exist where a given hole is very much oversize, we then defer to the owner's judgement as to whether perhaps dedicating a given barrel (or barrels) and a given frame combination due to a larger hinge pin requirement is warranted.

Brown makes an issue of the pin rotating in the holes. Our pins are precision centerless ground. IF they are an interference fit, at least one of the holes will prevent the pin from rotating in the first place, and IF per chance it still can rotate, such a change will make absolutely no difference in fit or accuracy. Again, ACTUAL, MEASURABLE HEADSPACE IS A SERIOUS ISSUE, AND ROTATION OF THE PIN IS THE LEAST ISSUE OF ALL, A NON-ISSUE.

I will add that in regard to a potential shifting of the pin side to side and impinging on the ears of the forend, IF our recommended "interference fit" is achieved in at least one of the three holes, the pin cannot rotate in that hole, nor can it slip side to side.

It should also be noted that while Cecil Epps deserves a lot of credit for bringing the side to side movement of the hinge pin with the resulting side pressure on the forend to our attention and addressing it with his headed "Locker Pin" that E.A.Brown markets, the "Locker Pin" does NOT tighten the fit at the hinge and is reported in some instances to be looser fitting than the stock TC factory hinge pins.

It is my experience, confirmed by tens of thousands of oversize hinge pin users over at least 20 years, that a loose fit at the hinge does in fact undermine accuracy while tightening the hinge improves accuracy or at least helps any given barrel shoot to its potential.

There is an overwhelming body of both sound machine shop practice and experiential evidence over many years in support of this approach, and if one gives it even a miniscule amount of serious thought, it only stands to reason that shake and rattle can't be conducive to accuracy. To blindly believe it is is, to be blunt, pardon my indiscretion, purely stupid